This invention relates to lightweight structures that can provide substantial sound transmission loss (STL) for frequencies in the audible range especially at lower audible frequencies and more specifically to the use of buttresses in cells in a honeycomb to control STL versus frequency response.
Common materials provide sound attenuation explained by the “mass law” which holds that sound transmission through a material is proportional to the product of its density, thickness and the frequency of the sound. A representative assumption of the mass law indicates that a doubling of either mass or frequency through a partition would result in only a 6 dB reduction of SPL through the medium (or an STL of 6 dB). Thus, for sound at a given frequency, lightweight materials (low density) that are relatively thin would not be expected to exhibit significant sound transmission (low STL). Although lightweight honeycomb structures have been described that provide sound attenuation not predicted by the mass law, it would be desirable to control the sound attenuation versus frequency response, preferably without having to change the dimensions of the honeycomb cells.